Tetraaquabis[2-(pyridin-4-yl-κN)pyrimidine-5-carboxylato]zinc

In the title complex, [Zn(C10H6N3O2)2(H2O)4], the ZnII ion lies on an inversion center and is coordinated in a slightly distorted octahedral geometry by two N atoms from two 2-(pyridin-4-yl)pyrimidine-5-carboxylate ligands and four water molecules. In the symmetry-unique part of the molecule, the pyridine and pyrimidine rings form a dihedral angle of 7.0 (1)°. In the crystal, the coordinating water molecules act as donor groups and carboxylate O atoms act as acceptors in O—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title complex, [Zn(C 10 H 6 N 3 O 2 ) 2 (H 2 O) 4 ], the Zn II ion lies on an inversion center and is coordinated in a slightly distorted octahedral geometry by two N atoms from two 2-(pyridin-4-yl)pyrimidine-5-carboxylate ligands and four water molecules. In the symmetry-unique part of the molecule, the pyridine and pyrimidine rings form a dihedral angle of 7.0 (1) . In the crystal, the coordinating water molecules act as donor groups and carboxylate O atoms act as acceptors in O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.
Data collection: SMART (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97. The aim of designing coordination frameworks is now been motivated through the field of supramolecular chemistry (Collet et al., 1996) and crystal engineering  from the viewpoints of the development of novel multifunctional MOFs. Fabricating MOFs with the desired properties are now the present day challenges of the chemist. N-Heterocyclic carboxylic acids share a major role in developing MOFs based material synthesis . Herein, we wish to report a new compound having an N-heterocyclic carboxylate ligand (2-pyridin-4-ylpyrimidine-5-carboxylato).
The molecular structure of the title compound is shown in Fig. 1. The Zn II ion lies on an inversion center and is coordinated in a slightly distorted octahedral geometry by two N atoms from two 2-pyridin-4-ylpyrimidine-5-carboxylato ligands and four water molecules. The equatorial plane is formed by the four water molecule and the two axial sites are occupied by the N-donor sites of the ligand. In the crystal, O-H···O hydrogen bonds form a three-dimensional network ( Fig. 2). The related structure, tetraaquabis[4-(4H-1,2,4-triazol-4-yl)benzoato-κN 1 ]manganese(II) decahydrate, has been published (Piao & Xuan, 2011).

Experimental
To prepare the complex we followed a routine hydrothermal process. Zn(NO 3 ) 2 hydrate and 2-pyridin-4-ylpyrimidine-5carboxylic acid were mixed in a 1:1 ratio, and kept in a reaction bomb at 433 K for 2 days in autogenously created pressure. After cooling to room temperature colourless block-shaped crystals were obtained. Yield ca. 45% (based on metal). The crystals were collected by filtration, washed thoroughly with water and dried in ambient conditions.

Refinement
The hydrogen atoms of the C-H bonds were placed at calculated positions and refined as riding atoms, with C-H = 0.95 Å with U iso (H) =1.2U eq (C) of the atom to which they are attached. The positions of the hydrogen atoms of the water molecules were discernible in difference Fourier maps and they were included in the structure refinement with individual isotropic thermal parameters and refined with an O-H distance restraint of 0.83 (2) Å.

Figure 2
Part of the crystal structure showing the three-dimensional hydrogen-bonded network.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.